Sec-phosphine dithiophosphinic acid salts

ABSTRACT

Zinc salts of hydrocarbyl-substituted or unsubstituted 9phosphabicyclononane-9,9-dithiophosphinic acid, useful as lubricating oil additives, are prepared by contacting 9-H-9phosphabicyclononane, optionally having one or more hydrocarbyl substituents on a ring carbon atoms, with sulfur in the presence of ammonium hydroxide, followed by treatment with a zinc salt.

United States Patent Morris et al.

[ 1 June 27, 1972 [54] SEC-PHOSPHINE DITHIOPHOSPHINIC ACID SALTS [72] lnventors: Rupert C. Morris, Berkeley; Ronald F.

Mason, Mill Valley, both of Calif.

[52] US. Cl ..260/429.9, 252/32.7 [51] Int. Cl. ..C07f 3/06 [58] Field of Search ..260/429.9

[56] References Cited UNITED STATES PATENTS 3,293,208 12/1966 Milionis et al. ..260/429.9 X 3,342,843 9/1967 Sandri ..260/429.9 3,351,647 11/1967 Butler et al. .....260/429.9

3,401,185 9/1968 Neinhardt ..260/4299 3,409,654 11/1968 Milionis et al. ..260/429.9

OTHER PUBLICATIONS Chemical Abstracts, Vol. 72, 30331: 1970).

Primary Examiner-Tobias E. Levow Assistant Examiner-H. M. S. Sneed Attorneyl-lenry C. Geller and Howard W. Haworth [57] ABSTRACT Zinc salts of hydrocarbyl-substituted or unsubstituted 9- phosphabicyclononane-9,9-dithiophosphinic acid, useful as lubricating oil additives, are prepared by contacting 9-H-9- phosphabicyclononane, optionally having one or more hydrocarbyl substituents on a ring carbon atoms, with sulfur in the presence of ammonium hydroxide, followed by treatment with a zinc salt.

4 Claims, No Drawings SEC-PHOSPHINE DITHIOPHOSPI-IINIC ACID SALTS BACKGROUND OF THE INVENTION The preparation of various dithiophosphinic acids from secondary phosphines by oxidation with excess sulfur has been reported by A. W. Hofmann and F. Mahla, Ber. 25, 2436 (1892) and I... Malatesta and R. Pizzotti, Gazz. Chim. Ital. 76, 167 (1946). G. Peters in US. Pat. No. 3,159,667 disclosed the preparation of secondary organophosphine sulfides by contacting equimolar amounts of sulfur and a secondary phosphine in an inert solvent and inert atmosphere.

SUMMARY OF THE INVENTION It has now been found that a novel class of lubricating oil additives is provided by the novel zinc salts of the 9-phosphabicyclononane-9,9-dithiophosphinic acids prepared by the reaction of certain 9-H-9-phosphabicyclononanes with sulfur in the presence of a base and subsequent treatment of the resulting product with a zinc salt. The acid precursors of the zinc salts incorporate a bicyclic heterocyclic ring system of eight carbon atoms and one phosphorus atom in a nonbridgehead position.

DESCRIPTION OF PREFERRED EMBODIMENTS H Hz? (ll-(CR2):

(CR2)y S=PSt2n 1120 C-- R2 J V H V 2 (I) where y and z are positive integers whose sum is 3 and R is hydrogen or alkyl. It is preferred that no more than two R groups be alkyl at any one time and that each of these be attached to a different ring carbon atom.

A particularly preferred group of bicyclic heterocyclic dithiophosphinic acid salts includes those wherein R is hydrogen or alkyl of 1-4 carbon atoms, that is, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, or tert-butyl. Particularly preferred are those compounds of the above formula 1 wherein each R is hydrogen.

A variety of substituted and unsubstituted 9-phosphabicyclononane dithiophosphinic acid salts may be produced. In the nomenclature of such compounds, as well as the reactants employed for the production thereof, conventional numbering of the ring systems has been employed, as further illustrated by the following formulas:

The bicyclic compounds of the invention are produced in a two step process by reacting certain phosphines with sulfur in the presence of a base and then converting the resulting initial product to the corresponding zinc salt.

H2O C(CRH) I (CRH)y PH H1O C(C RH) where y and z are positive integers whose sum is 3 and R is hydrogen or lower alkyl of from one to four carbon atoms, such that no more than two R groups are alkyl at any one time and each of the alkyl groups is attached to a different ring carbon. Representative examples of these 9-H-9-phosphabicyclononanes include 9-H-9-phosphabicyclo(3.3.1)nonane; 2,6-dimethyl-9-phosphabicyclo-(4.2.1 )nonane; 3,8-dimethyl- 9-H-9-phosphabicyclo(3.3.l)nonane, and the like. Preferred are 9-H-9-phosphabicyclo(4.2.l)nonane and 9-H-9- phosphabicyclo( 3.3. l )nonane.

The first step of the reaction, sulfurization of the secondary phosphine, is carried out by contacting the secondary phosphine with sulfur in the presence of a base, preferably ammonium hydroxide. Oxygen is excluded from the reaction zone, to minimize the oxidation of the phosphine to phosphinic acid. In a preferred embodiment, the reaction is carried out in an inert atmosphere, such as under nitrogen, argon, helium, or the like, or, when the reactants are sufficiently high boiling, under vacuum.

A molar'excess of sulfur with respect to the secondary phosphine is used in the sulfurization reaction. Preferably, at least two molar equivalents of sulfur are present for each molar equivalent of the secondary 9-phosphabicyclononane in order to minimize the formation of undesired secondary 9- phosphabicyclononane sulfides. The reaction is conducted in the presence of an inert diluent such as water, ethanol, petroleum ether, dimethoxyethane, and the like. The diluent should be free of substances, such as air or oxygen, capable of converting the bicyclic heterocyclic phosphines to a higher oxidation state. If desired, small amounts of oxidative inhibitors may be added.

The temperature at which the reaction is conducted will in part be governed by the decomposition point of the bicyclic heterocyclic phosphine reactant and of the initial reaction product, an ammonium salt of the corresponding 9-phosphabicyclodithiophosphinic acid. The lower temperature limit is that at which the sulfurization becomes impractically slow. Temperatures from 0 to C may be used with the preferred range ordinarily being 15 to 75 C. The reaction is usually carried out at atmospheric pressure, although higher or lower pressures may be used, with due consideration given to the physical properties of the reactants, e.g., volatility and the like, as mentioned previously.

The crude initial product containing the ammonium salt of alkyl-substituted or unsubstituted 9-phosphabicyclononane- 9,9-dithiophosphinic acid may be used as a starting material for the second step of the process without further purification or it may be isolated and purified by conventional means such as crystallization, extraction or absorption.

In the second step of the process, a zinc salt is reacted with the intennediate ammonium salt of the alkyl-substituted or unsubstituted 9-phosphabicyclononane-9,9-dithiophosphinic acid prepared in the first step of the process. The zinc salt used is any ionic zinc salt, such as zinc halide, zinc nitrate, zinc sulfate, zinc acetate and the like. Preferred salts are zinc chloride and zinc bromide.

A molar excess of the intermediate phosphinic acid ammonium salt is contacted with the zinc salt. Preferably, two

molar equivalents of the phosphinic acid salt are employed per molar equivalent of zinc salt in order to obtain a maximum yield.

The reaction is carried out in the presence of an inert reaction diluent, such as water.

The temperature at which the second step of the reaction sequence is carried out will also be governed by the decomposition points of the reactant ammonium salt and the product zinc salt. The lower limit on temperature is that at which the reaction proceeds impractically slowly. Temperatures from to 100 C may be used, with the preferred range ordinarily being to 75 C.

While atmospheric pressures are desirable for the reaction of the ammonium salt of the 9-phosphabicyclononanes-9,9- dithiophosphinic acid with the zinc salt, superand sub-atmospheric pressures are also suitable.

The zinc salts of the 9-phosphabicyclononane-9,9- dihiophosphinic acids of this invention are recovered and purified by any conventional means known in the art such as filtration and recrystallization. A variety of substituted and unsubstituted 9-phosphabicyclononane dithiophosphinic acid salts may be produced. Typical products of the process of the invention are 9-phosphabicyclo[4.2.1 ]nonane dithiophosphonic acid salts, for example the zinc salt of 9- phosphabicyclo[4.2.lnonane-9,9-dithiophosphinic acid; the zinc salt of 3,7-dimethyl-9-phosphabicyclo[4.2. l ]nonane-9,9- dithiophosphinic-acid, the zinc salt of 9-phosphabicyclo[3.3.1 ]nonane-9,9-dithiophosphinic acid, the zinc salt of 3,8- dimethyl-9-phosphabicyclo[4.2. l ]nonane-9,9-dithiophosphinic acid; the zinc salt of 3,7-dimethyl-9-phosphabicyclo[ 3.3.1]n0nane-9,9-dithiophosphinic acid; the zinc salt of 3,8- dimethyl-9-phosphabicyclo[ 3 .3. l ]nonane-9,9-dithiophosphinic acid, and the like. Preferred products are the zinc salt of 9-phosphabicyclo[4.2. l ]nonane-9,9-dithiophosphinic acid and the zinc salt of 9-phosphabicyclo[3.3.l]nonane-9,9- dithiophosphinic acid.

The novel compounds of the invention are particularly useful as multipurpose additives for lubricating oils.

The lubricating oil in the lubricating compositions of the invention can be any natural or synthetic oil having lubricating properties. Thus, the oil can be a hydrocarbon lubricating oil obtained from paraffinic or naphthenic crude or mixtures thereof. The viscosity of these oils may vary over a wide range, such as from 50 SUS at 100 F to 300 SUS at 210 F. If desired, the synthetic lubricating oils may be used as the sole base lubricating oil or admixed with fatty oils or derivatives thereof or synthetic lubricating oils. For example, the hydrocarbon lubricating oil may be blended with fatty oils such as castor oil or lard oil, and/or with synthetic lubricating oils such as polymerized olefins, copolymers of alkylene glycols and alkylene oxides, organic esters, e. g., di( 2-ethylhexyl)sebacate, dioctyl phthalate and trioctyl phosphate and polyalkyl silicone polymers such as dimethyl silicone polymers.

It will be understood that the lubricating compositions of the invention may be modified by the addition thereto of minor proportions of other additives such as metal dithiophosphates, e.g., zinc di-2-ethylhexyl dithiophosphate, metal organic sulfonates, e.g., neutral or basic calcium, barium or zinc petroleum sulfonate; metal thiocarbonates, e.g., zinc, chromium or calcium dibutyl or diamyl dithiocarbamate; amines, e.g., phenyl-alpha-naphthylamine or octadecylarnine; alkylated phenols and alkylated bisphenols, e.g., 2,6-ditertiary-butyl-4-methylphenol, 2,6-ditertiarybutyl-4-hydroxybenzyl alcohol and 4,4'-methylene bis(2,6-ditertiarybutylphenol); organic sulfides, e.g., dibenzyldisulfide, VI improvers, e.g., methacrylate polymers, e.g., the Acryloids 150 or 710.

According to the present invention, lubricating compositions are provided which comprise a major amount of a lubricating oil and a minor amount of from about 0.01 to 2 percent and preferably from about 0.02 to 0.15 percent by weight of the novel 9-phosphabicyclononane-9,9-dithiophosphinic acid zinc salts.

To further illustrate the novel products of the invention and the use of the novel products in lubricating oil compositions, the following examples are provided. It should be understood that they are not to be regarded as limitations, as the teachings thereof may be varied as will be understood by one skilled in the art.

EXAMPLE I A 500 ml reaction flask with stirrer, thermometer, reflux condenser, dropping funnel and nitrogen inlet was charged with 7.1 grams (0.22 moles) of sulfur, 60 ml concentrated ammonium hydroxide, 60 ml distilled water and 40 ml ethanol. The mixture was stirred magnetically and a nitrogen blanket maintained at all times. A solution of 14 grams (0.1 mole) of a resublimed mixture of 9-H-9-phosphabicyclo[4.2.1]nonane and 9-H-9-phosphabicyclo[3.3.l]nonane in 30 ml of 1,2- dimethoxyethane was added dropwise over a period of 45 minutes. The temperature of the reaction flask was maintained at 2535 C. After all the 9-H-9-phosphabicyclononane has been added, the reaction mixture was heated to 55 C and stirred for l 2% hours.

After standing for 2 days, 2.5 grams of insoluble material was removed by filtration and the solvents removed under reduced pressure at 45 C. 19 grams of a mixture of crude, water soluble ammonium 9-phosphabicyclo[4.2.l ]nonane- 9,9-dithiophosphinate and ammonium 9-phosphabicyclo[3.3.1]-nonane-9,9-dithiophosphinate in 86 percent yield was obtained. The structure of the product was determined by preparation of the novel bis(9-phosphabicyclononane-9-thioyl)disulfide and by elemental analysis.

Anal.-Calculated for C H NPS C, 43.0; H, 8.1; N, 6.3; P,

13.9; S, 28.7; Found: C, 41.7; H, 8.6; N, 5.9; P, 13.7; S, 25.0.

EXAMPLE ll The mixture of 71 grams of ammonium 9-phosphabicyclononane-9,9-dithiophosphinates prepared in Example I were dissolved in 250 ml water at 50 C and filtered to remove 1.7 grams of insoluble material. A solution of 22 grams zinc chloride in ml water was added to the clear filtrate. An additional 200 ml water was added and the solution stirred for 1 hour. The product formed a white, curdy precipitate that was filtered and washed well with water. The residue was dried overnight in a vacuum oven at 40 C to yield 68.5 grams (88.5 percent yield) of a mixture of zinc 9-phosphabicyclo[4.2.l]- nonane-9,9-dithiophosphinate and zinc 9-phosphabicyclo[ 3.3. l ]nonane-9,9-dithiophosphinate, melting at 286-300 C with decomposition.

Anal.Ca.lculated for (C H PS Zn: Zn, 13.7.

Found: Zn, 13.2.

EXAMPLE Ill Lubricating compositions of this invention were evaluate as extreme pressure agents by use of the Four-Ball Wear Tester.

In conducting this test, a precision four ball wear test machine is employed. This machine is designed so that three balls are fixed in a horizontal plane in a cup while a fourth ball which is movable is rotated in a fixed position contacting the other three balls to form an equilateral tetrahedron. The test cup is placed on a stage which can move vertically to facilitate loading. The stage rests on a calibrated fulcrum so that specific weights may be applied to force the three balls in the cup to contact the rotating fourth ball at a predetermined pressure. The cup holding the three balls also contains the test lubricant at a level of 2 mm above the balls, thus assuring an adequate supply of lubricant at the contact points. A fixed oil temperature is maintained by a relay system connected to thermocouple in the cup and a heater in the stage. The fourth ball can be rotated from a motor drive at 600, 1,200, or 1,800 rpm. Each test is run with new steel balls.

A test is run on a lubricant at a specific load, temperature speed and time. Lubricating properties are evaluated from l) the diameter of the scars on the three balls and (2) on the load in kilograms at which seizure occurs. A more complete description of the machine and test method are given in the Naval Research Laboratory Report entitled A Study of the Four Ball Wear Machine," by W. C. Clinton, NRL Report 3709, September 1950.

The precision four ball wcar test was used to illustrate the improved load-carrying characteristics of a composition of the invention. The movable ball was rotated at 600 r.p.m. for two hours at a lever load of 30, 40 and 50 kilograms. The test lubricant was maintained at 200 F. The lubricants which were tested consisted of a mineral oil having viscosity of about 250 SUS at 100 F and the same base oil containing 0.1 percent by weight of the mixture of the salts of 9-phosphabicyclo[4.2.l ]nonane-9,9-dithiophosphinate and 9-phosphabicyclo[3.3.l

]nonane-9,9-dithiophosphinate, designated Dithiophosphinate salt" in the tables below.

TABLE I Four-Ball Wear Test Additive The oxidation resistance of the lubricants of this invention is shown by the results of the Air Oxidation Test summarized in Table III. The test consists of measuring the length of time necessary for the lubricating oil to absorb 1.0 millimole of oxygen per gram of oil at 350 F in the presence of 20 parts per million of a soluble iron catalyst.

TABLE 111 Air Oxidation Test Additive Oxidation Life, Hours none 5.5 Dithiophosphinate salt 49.0

We claim as our invention: 1. Zinc 9-phosphabicyclononane-9,9-dithiophosphinic acid 

2. The 9-phosphabicyclononane-9,9-dithiophosphonic acid salts of claim 1 wherein each R is hydrogen.
 3. The 9-phosphabicyclononane-9,9-dithiophosphinic acid salt of claim 2 wherein y is 2 and z is
 1. 4. The 9-phosphabicyclononane-9,9-dithiophosphinic acid salt of claim 2 wherein y is 1 and z is
 2. 